Nice tut, but there is a way more compact and easy method of doing so requiring:
1 Dispenser
1 Redstone
2 Redstone Torches
1 Redstone Repeater
1 Lever
3 Basic Blocks (assuming you have a solid ground).
Assemble it like so: (Front view, but obviously the lever would be at the back.
PS: The red line is a single redstone dust.

The repeater is at a 3 setting to prevent burnout, but you can still utilize all time settings (you'll just have to reset by hitting the lever twice). The top redstone torch is for rapid fire, and the clock has a torch powering a block, powering a repeater, powering the dispenser. At the same time as it powers the dispenser, the redstone dust is also powered, and that redstone powers the original torch, repeating the cycle.